Imaging Integrin α_vβ₃ on Blood Vessels with ¹¹¹In-RGD₂ in Head and Neck Tumor Xenografts

Abstract

Arginine-glycine-aspartic acid (RGD)-based imaging tracers allow specific imaging of integrin a v b 3 , a protein overexpressed during angiogenesis, leading to the possibility that it might serve as a tool to stratify patients for antiangiogenic treatment. However, these tracers have generally been characterized in xenograft models in which integrin a v b 3 was constitutively expressed by the tumor cells themselves. In the studies presented here, the use of 111 In-RGD 2 as a tracer to image only integrin a v b 3 expression on blood vessels in the tumor was determined using tumor xenografts in which tumor cells were integrin a v b 3 -negative. Methods: DOTA-E-[c(RGDfK)] 2 was radiolabeled with 111 In ( 111 In-RGD 2 ), and biodistribution studies were performed in squamous cell carcinoma of the head and neck (HNSCC) xenograft mouse models to determine the optimal peptide dose to image angiogenesis. Next, biodistribution and imaging studies were performed at the optimal peptide dose in 3 HNSCC mouse models, FaDu, SCCNij3, and SCCNij202. Immunohistochemical analysis of tumor vascular and cell surface expression of integrin a v b 3 and correlation analysis of vascular integrin a v b 3 and autoradiography were completed. Results: All 3 HNSCC xenografts expressed integrin a v b 3 on the vessels only. The optimal peptide dose of 111 In-RGD 2 was 1 mg or less for specific integrin a v b 3 -mediated uptake of the tracer. SPECT/CT imaging showed clear uptake of the tracer in the periphery of the tumors, corresponding with wellvascularized areas of the tumor. Within the tumor, 111 In-RGD 2 autoradiography coincided with vascular integrin a v b 3 expression, as determined immunohistochemically. Integrin a v b 3 -mediated uptake was also detected in nontumor tissues, which, through immunohistochemical analysis, proved positive for integrin a v b 3 . Conclusion: 111 In-RGD 2 allows the visualization of integrin a v b 3 in xenograft models in which integrin a v b 3 is expressed only on the neovasculature, such as in the HNSCC tumors. Thus, 111 In-RGD 2 allows specific visualization of angiogenesis in tumor models lacking constitutive tumoral integrin a v b 3 expression but may be less useful for this purpose in many tumors in which tumor cells express integrin a v b 3 .

Monitoring Therapy Response of Experimental Arthritis with Radiolabeled Tracers Targeting Fibroblasts, Macrophages, or Integrin αvβ3

“…In previous studies, the authors did not see accumulation of any of the tracers in the joints of nonarthritic mice (8,12,13,18). The 3 tracers are different with regard to their targets, mechanism, and pharmacokinetics; they all measure something different, so a straight comparison was not performed here.…”

“…Preclinically, F4/80 receptor-positive macrophages also play a role in arthritis pathogenesis (11). These targets have previously been successfully imaged by either radiolabeled RGD-based peptides (12) or an anti-F4/80-A3-1 labeled with 111 In (13), albeit in an oncologic setting.…”

Can 111In-RGD2 Monitor Response to Therapy in Head and Neck Tumor Xenografts?

“…When tumors reached 200 mm 3 , anesthetized mice (isoflurane/air/O 2 , 5% induction, 3% maintenance) were covered in custom-made lead shielding, to locally irradiate the tumor only, at 10 Gy using a 320 kV X-RAD system (RPS Services Limited) at 3. . Purification and quality control were also performed as described previously to ensure that a radiochemical purity of 95% was achieved (14).…”

“…The validation of RGD-based imaging probes often included in vivo tumor xenograft models in which integrin a v b 3 was constitutively overexpressed on tumor cells (6)(7)(8)(9)(10)(11)(12)(13). More recently, radiolabeled DOTA-E-[c(RGDfK)] 2 was also shown to allow imaging of angiogenesis itself, when used in a tumor model in which integrin a v b 3 was expressed solely on the tumor vasculature (14).…”

“…The novelty is the use of tumor models in which integrin a v b 3 is expressed only on angiogenic blood vessels (14). We also investigated the use of 111 In-RGD 2 as a tool to monitor antiangiogenic therapy in integrin a v b 3 -positive tumors (22).…”